Ubuntu – Workflow to commit file to remote branch in a PR

I have a repo with a main branch and a testing branch. I make modifications in the testing branch, push, open a PR. This triggers the following workflow (borrowed from https://stackoverflow.com/a/73687159/659117) which creates a file (e.g. a PDF from latex files) and commits it:

name: Example workflow
on:

  pull_request:
    branches: [ main ]

jobs:
  example_job:
    runs-on: ubuntu-latest

    permissions:
      contents: write

    steps:
      - uses: actions/checkout@v4
        with:
          ref: ${{ github.head_ref }}
      - shell: bash
        run: |
          date > 1.txt
          git config user.name github-actions
          git config user.email [email protected]
          git add 1.txt
          git commit -m "updated"
          git push origin HEAD:${{ github.head_ref }}

So far, so good: the file 1.txt is created and added to the branch testing, and I can see the commit in the PR.

However, if I now make another change to the code (locally) and push it, the commit is rejected with the error:

hint: Updates were rejected because the remote contains work that you do not
hint: have locally. This is usually caused by another repository pushing to
hint: the same ref. If you want to integrate the remote changes, use
hint: 'git pull' before pushing again.

I know I can override it by doing push -f, but it is not something I want to do on a regular basis. So I would I set up a workflow that does this, without running into this problem? Am I missing something here?